Abstract: We introduce here a new photochemical probe suitable for labeling deep into the hydrophobic core of membranes: bis-phosphatidylethanolamine (trifluoromethy1) phenyldiazirine 19 (DIPETPD). This is a bipolar phospholipid provided with a covalently bonded chain designed to span the membrane and equipped with a centrally defined attachment point for the photolabeling group (trifluoromethy1) phenyldiazirine (TPD). This ...